In many sputter deposition processes, particularly reactive processes such as those used to deposit materials such as titanium nitride onto stepped and other three dimensional features of semiconductor wafers, it is necessary to provide a controlled flow of gas along the surface of the wafer to be coated. This flow of gas is necessary, particularly in reactive deposition processes, to bring an adequate supply of fresh gas into contact with the wafer and to flush away spent gas from the wafer surface that might interfere with the reactive process that forms the coating.
For example, in the deposition of titanium nitride sputtered films, titanium metal is sputtered from a metallic titanium target onto the surface of a substrate to be coated. At the surface, which is maintained at a controlled reaction temperature of from about 200.degree. C. to about 450.degree. C., nitrogen gas is brought into contact with the titanium to form the film of titanium nitride.
In sputter deposition processes, a plasma is created, usually in an inert gas such as argon, adjacent a target formed of the material that is to become at least a part of the coating. By developing an electric potential between the plasma and the target, ions are produced in the inert gas that physically bombard the target and dislodge the sputtering material, causing the sputtered material to propagate to the surface of a substrate to be coated.
In titanium nitride deposition, such targets are typically of titanium metal and are bombarded with inert argon ions. Nitrogen gas, which is essential in such a process at the surface of the substrate, is an undesirable element at the surface of the target where it may react to form titanium nitride that inhibits the sputtering of titanium metal, slowing the sputter deposition process. Generally, in reactive sputter deposition processes, the target is bombarded with ions from an inert gas, and the dislodged particles brought into contact with the substrate in the presence of a reactive gas, which brings about a reaction that produces the final coating or causes it to bond to the surface. Usually, such a reactive gas produces undesirable results whenever brought into contact with the surface of the target.
In sputter coating processes, particularly for coating stepped semiconductor wafers, it is desirable to control the directionality of the propagating sputtered particles onto the substrate. One such way for controlling the flux onto the substrate is to interpose a collimator between the substrate and the target. Such a collimator is provided with a grid or other such structure having openings therethrough that permit the passage of particles in certain directions and shadow particles passing in other directions. As a result, coatings can be formed through a collimator at the bottoms of vias of improved thickness relative to the sides. Such collimators aid in the distribution of the coating onto three dimensional features of the substrate surface, and may also be used to control the uniformity of the produced film on the substrate surfaces.
In sputter coating processes, it is desirable to bring gasses into contact with the surface of the substrate by directly communicating the gas onto the substrate. The problem this presents is that the means for delivering the gasses to the areas where they are needed on the substrate may shadow the surface of the substrate and interfere with the distribution of sputtered film onto the substrate from the target.
Thus, there is a need for delivering reactive or other sputtering gas onto a substrate surface without undesirably shadowing the surface to be coated from the sputtered material.